This invention relates to a process for producing 5-methyl-N-aryl-2-pyrrolidone, 5-methyl-N-cycloalkyl-2-pyrrolidone, and 5-methyl-N-alkyl-2-pyrrolidone by reductive amination of levulinic acid with nitro compounds utilizing a metal catalyst, which is optionally supported.
Levulinic acid is a well-known product of hexose acid hydrolysis, and can be inexpensively obtained from cellulose feedstocks. Consequently, it is an attractive starting material in producing many useful 5-carbon compounds and their derivatives. For example, N-cyclohexyl-2-pyrrolidone is used as a solvent or intermediate in many industrial applications, including the electronics industry (photo-resist stripping solutions), industrial cleaners, oil /gas well maintenance, and fiber dyeing. N-[2-hydroxyethyl-]2-pyrrolidone is useful in industrial cleaning, printing inks, and gasoline and oil additives. N-octyl-2-pyrrolidone is useful, for example, in the manufacture of agricultural products, as a detergent and dispersant, in industrial and metal cleaners, in printing inks and in fiber dyeing.
Emmert (Ber. d. deutschen chemischen Gesellschaft, 1907, 40: 912) describes a process for producing 5-methyl-1-phenyl-pyrrolidone by simultaneous electrolytic reduction of levulinic acid and nitrobenzene. The reaction was carried out for 5-22.5 hr at a quantity of current and temperature of 90 ampere-hours and 16xc2x0 C. to 33xc2x0 C., respectively. This process is complex and yields only the phenyl derivative. U.S. Pat. No. 3,337,585 discloses a process for preparing 5-methyl-1-alkyl-2-pyrrolidone utilizing levulinic acid and a primary alkyl amine at a temperature of 50xc2x0 C. to 350xc2x0 C. under carbon monoxide at a pressure of 1.0 to 101 MPa. Additional potential primary amines include alkylene diamines, aryl amines and cycloalkyl amines. Compounds containing NO2 groups are not used. U.S. Pat. No. 3,235,562 describes a vapor phase process for producing lactams by the reductive amination of oxo carboxylic acid compounds. Volatile alkyl or aryl primary amines may be used; nitro compounds are not used. Candeloro and Bowie (Aust. J. Chem., 1978, 31:2031-2037) describe a process for producing 5-methyl-2,3-dihydro-1-H-benzazepin-2-one and 5-(2-methyl-5-oxo-1-phenylpyrrolidin-2-yl)4-oxo-N-phenylpentanamide by reacting levulinic acid with aniline under a nitrogen atmosphere.
An efficient and low cost process for the production of aryl, alkyl and cycloalkyl pyrrolidones would be advantageous.
The present invention is a novel, one-step process for converting levulinic acid and nitro compounds to aryl, alkyl and cycloalkyl pyrrolidones as set forth in greater detail below in the presence of catalysts. Specifically, the present invention relates to a process for preparing 5-methyl-N-aryl-2-pyrrolidone (III), 5-methyl-N-cycloalkyl-2-pyrrolidone (IV), or a mixture thereof, which comprises the step of contacting the compound levulinic acid (I) with an aryl nitro compound (II) in the presence of a catalyst and hydrogen gas; 
wherein R1 is an aromatic group having from 6 to 30 carbons and R2 is a fully or partially reduced derivative of R1, and wherein 5-methyl-N-aryl-2-pyrrolidone (III), 5-methyl-N-cycloalkyl-2-pyrrolidone (IV), or a mixture thereof, may comprise 100% by weight of the total product formed, or wherein additional products may be produced.
The catalyst useful in the process of the invention is selected from metals from the group consisting of palladium, ruthenium, rhenium, rhodium, iridium, platinum, nickel, cobalt, copper, iron, osmium; compounds thereof; and combinations thereof.
The present invention also relates to a process for preparing 5-methyl-N-alkyl-2-pyrrolidone (VI) which comprises the step of contacting levulinic acid (I) with an alkyl nitro compound (V) in the presence of a catalyst and hydrogen gas; 
wherein R3 is an alkyl group having from 1 to 30 carbons and R3 may be C1-C30 unsubstituted or substituted alkyl, C1-C30 unsubstituted or substituted alkenyl, C1-C30 unsubstituted or substituted alkynyl, C3-C30 unsubstituted or substituted cycloalkyl, or C3-C30 unsubstituted or substituted cycloalkyl containing at least one heteroatom, and wherein 5-methyl-N-alkyl-2-pyrrolidone (VI) may comprise 100% by weight of the total product formed, or wherein additional products may be produced.
The catalyst useful in this process of the invention is selected from metals from the group consisting of palladium, ruthenium, rhenium, rhodium, iridium, platinum, nickel, cobalt, copper, iron, osmium; compounds thereof; and combinations thereof.